The Samsung dishwasher drain check valve is located underneath the dishwasher, just before the drain hose. It's a one-way valve, allowing water to drain but not return to the dishwasher. It is made of black plastic and is approximately 1-1/4 inches by 1-1/4 inches. The round section of the check valve is approximately 1 inch in diameter. The drain check valve prevents dirty water from re-entering the dishwasher once it has been pumped out. Remove the drain hose from the dishwasher (remembering to put a drain pan underneath) and check to make sure the valve is clean and opens.